Life History Life history - An organism's life history is its lifetime pattern of growth, differentiation, storage of energy and most importantly, its reproduction.

Life Histories vary among species Life history variation in plants has to do with the lifespan and how many times it will reproduce. annuals- Go from seed to seed in less than 12 months. Life cycle is competed in one growing season. biennials – 1) a season of vegetative growth and storage of photosynthate in the roots followed 2) by a season of reproductive output –flowers  seed. perennials - Live for more than two years, then reproduce for many years.

Life Histories vary among species A century plant – Grows for many seasons – Reproduces in years – Reproduces only once

Life Histories vary among species A dandelion – Germinates and grows one season. – Continues to grow the next season. – Reproduces once.

Life Histories vary among species Broccoli – Germinates and grows in one season. – Reproduces once.

Life Histories vary among species An oak tree -Germinates and grows many seasons -Reproduces many times

Life Histories vary among species Animals do not have well-defined growth periods like plants years in the ocean “big-bang” reproduction

Life Histories vary among species Red kangaroos can simultaneously care for 3 young at once. Joey in pouch, 7-9 months Joey out of pouch A baby on a teat garoo-nursing/

Life Histories vary among species Reproductive periodicity itero – repeat; parous – bearing, producing semel – once; parous – bearing, producingSemelparous - Iteroparous -

Reproductive Value V x is the contribution an average individual aged x will make to the next generation before it dies. t and x - age w – age at last reproduction

Reproductive Value Reproductive value of the annual Phlox drummondii. Age Classes – The year during which this annual lives has been divided up into 12 age classes that are not uniform in time. l x – is age-specific survivorship from a life table b x – is age-specific birth rate from a life table RRV – the Residual Reproductive value is Reproductive Value

Age ClassDayslxlx bxbx RRVVxVx

Reproductive Value – graphically

Reproductive Value – in words Phlox drummondii slowly increases V x with age, then declines. V x is low for young individuals when they have only a low probability of surviving to reproductive maturity. If survivorship of young plants is low, there is less benefit from reproduction and selection favors a lower V x at a young age Recall trade-offs; reproduce a little, or survive and reproduce a lot later. Therefore, high juvenile mortality increases RRV. The probability of reproducing in the future is greater. BUT –only if it brings with it either an improvement of survivorship of young plants or a compensatory increase in adult longevity and probability of future reproduction. V x steadily increases as the age of first reproduction is approached. It becomes more and more certain that surviving individuals will reach reproductive maturity. V x is low again for older individuals because of reproductive opportunities left behind and declines in fecundity or survival.

Reproductive Value – Pediculus humanus For organisms that breed only once – T = average time from egg to egg. For repeated reproducers - T = mean generation time: the average parental age at which all offspring are born.

Reproductive Value

Phlox drummondii slowly increases V x with age, then declines. V x is low for young individuals when probability of surviving to reproductive maturity is low. If survivorship of young plants is low, there is less benefit from reproduction and selection favors a lower V x at a young age but only if it brings with it either an improvement of survivorship of young plants or a compensatory increase in adult longevity and probability of future reproduction. V x steadily increases as the age of first reproduction is approached. It becomes more and more certain that surviving individuals will reach reproductive maturity. V x is low again for older individuals because of reproductive opportunities left behind and declines in fecundity or survival.

Reproductive Value Acacia suaveolens When the extrinsic death rate (death independent of reproduction) for older plants is high compared to young plants, then the number of reproductive attempts is limited. Earlier reproduction is selected for, since any plant that waits to reproduce at the expense of current production is likely to have fewer offspring than those that don't. High adult mortality lowers RRV- the probability of reproducing in the future is reduced.

Reproductive Value – why V x is not maximized Tradeoffs in the demand for photosynthate. Pseudotsuga menziesii - Trade-off between growth and reproduction.

Reproductive Value - why V x is not maximized all the time Tradeoffs in the demand for photosynthate. Poa annua – tradeoff between current and future reproduction.

Reproductive Value

Life History Traits of Plants I did not cover these traits in lecture.